According to a recent study, trilobites, ancient marine arthropods that lived from 520 million years ago until their extinction 250 million years ago at the end of the Permian epoch, may have developed similarly to modern crustaceans and reached ages that are comparable to them.
Relationship of trilobites to modern crustaceans
Pavel Polívka/Unsplash
Researchers from the University of British Columbia and Uppsala University demonstrated in a study that was published in the journal Paleobiology that the Ordovician trilobite, Triarthrus eatoni, which lived 450 million years ago, reached a length of just over four centimeters in about 10 years, and had a growth curve resembling to that of small, slow-growing crustaceans.
T. eatoni lived in low-oxygen environments and, like extant crustaceans exposed to hypoxic conditions, showed low growth rates compared with growth under more oxygenated conditions, according to Daniel Pauly, principal investigator of UBC's Sea Around Us initiative and lead author of the study, as cited by ScienceDaily.
Low-oxygen environments make it harder for water breathers to develop and add to the challenges of inhaling through gills, which, as 2D surfaces, cannot keep up with their 3D bodies.
Therefore, in order to sustain the remainder of their bodily processes under hypoxic conditions, they must continue to be little.
Trilobites had exopods, which were external branches on the tops of their limbs, which served as gills.
Therefore, the development restrictions on these extinct species were comparable to those on their living relatives.
Pauly and paleontologist James Holmes, a colleague from Uppsala University, used the analysis of length-frequency data, a technique created in the fields of fisheries science and marine biology for examining the growth of fish and invertebrates lacking the physical markings that serve as age markers.
The zoological affiliations of trilobites may be established from features retained in fossils despite a quarter billion years since their demise, as per the Australian Museum.
Trilobita were generally known to belong to the Arthropoda before the first trilobite with its legs fossilized was reported in 1870.
Since the Early Cambrian, arthropods have been the most varied phylum of multicellular organisms and have the greatest number of species.
Their primary subdivisions include the crustaceans, which include millipedes and centipedes; the chelicerates, which include spiders, scorpions, and mites; and the entirely terrestrial families Insecta and Myriapoda.
The group of extinct arthropods with the largest species diversity is the trilobita.
The hard exoskeleton that covered the dorsal body surface of trilobites and its distinct segmentation (such as the jointed segments of the thorax) are typical arthropod characteristics.
The calcite-based trilobite exoskeleton was mineralized.
The labrum, a similar feature seen in other arthropods, is analogous to the trilobite hypostome, a plate affixed to the lower side of the head right in front of the mouth opening.
Most trilobites have two compound eyes, and the way their ommatidia are arranged is typical of arthropods.
To accommodate development, trilobites regularly shed their exoskeleton.
Trilobite fossils occasionally contain so-called molt configurations, which depict different phases of the animal's exoskeleton being released and its subsequent escape.
Another defining trait of arthropods is molting. The majority of trilobites shed their skin by severing the head shield at weak points (known as facial sutures) that run parallel to the eye's visible surface.
